1. Field of the Invention
The present invention relates to a semiconductor device which is configured to expose the back of a semiconductor element mounting pad to the outside of a package.
2. Description of the Related Art
In order to favorably release heat and electromagnetic noise generated as semiconductor element B is made to have a large size and large capacity, and to achieve thinning of package P, semiconductor device A shown in FIG. 5 has pad C which mounts the semiconductor element B and which is down set and the back of the pad C is exposed to the outside of package P.
In the semiconductor device A, the semiconductor element B and leads L, L, . . . are connected by bonding wires W, and in order to use the pad C as a ground, the entire surface of the pad C is plated with a noble metal such as Ag (silver), and the semiconductor element B and the pad C are bonded by bonding wires (ground bonding wire) G for grounding.
Meantime, the aforesaid semiconductor device A has a disadvantage that moisture is easy to enter into it through boundary part V between the pad C and the package P because the pad C is exposed to the outside of the package P, and when moisture reaches a semiconductor element-mounting surface of the pad C and evaporated or expanded as the semiconductor device A is heated, a popcorn crack might be caused.
It also has a disadvantage that since the pad C of the semiconductor device A has its large area exposed to the outside of the package P, it is directly affected by heat when the semiconductor device A is exposed by a heat cycle of heating and cooling to cause a gap at the boundary part V between the pad C and the package P due to a difference in heat expansion rate, and moisture is allowed to enter through the gap.
Furthermore, there is a disadvantage that the noble metal-plated surface on the entire surface of the pad C is poor in intimate contact with the package (sealing resin) P as compared with a non-plated surface, so that when the semiconductor device A is exposed to a heat cycle, broad peeling is caused between the pad C and the package (sealing resin) P to break any of the bonding wires (ground bonding wire) G.
There is also a disadvantage that when epoxy resin-based adhesive agent F used to fix the semiconductor element B to the pad C is precipitated to the surface of the pad C due to heating to form a bleed layer, broad peeling is also caused between the pad C and the package (sealing resin) P to break any of the bonding wires (ground bonding wire) G.
In view of the aforesaid circumstances, it is an object of the present invention to provide a semiconductor device which can prevent moisture from entering the package and also can prevent peeling between the pad and the package from occurring.
The semiconductor device of claim 1 according to the present invention is a semiconductor device in which a back of a pad for mounting a semiconductor element is exposed to an outside of a package, comprising: grooves formed on a semiconductor element mounting surface of the pad to surround the semiconductor element; plated portions formed on only a ground bond area of the semiconductor element mounting surface of the pad; a thin portion formed on an entire peripheral edge portions on the back of the pad; and thin portions formed at portions, which connect with the pad, on backs of support bars extending from the pad.
By configuring as described above, an unexpected gap can be prevented from being formed at the boundary between the pad and the package, and a route of moisture at the boundary between the pad and the package becomes long, so that moisture can be prevented from entering into the semiconductor element-mounting surface of the pad, and a popcorn crack can be prevented from occurring.
And, by configuring as described above, an adhesive agent does not flow to expand to all the area of the semiconductor element-mounting surface of the pad, and plated portions having poor adhesion with the package are formed on only a minimum ground bond area. Therefore, extensive peeling between the package and the pad can be prevented, and bonding wires are prevented from being broken.